Oncogenes frequently encode protein components of signal transduction pathways, which lead to stimulation of cell growth and mitogenesis. Oncogene expression in cultured cells leads to cellular transformation, characterized by the ability of cells to grow in soft agar and the growth of cells as dense foci lacking the contact inhibition exhibited by non-transformed cells. Mutation and/or overexpression of certain oncogenes are frequently associated with human cancer. A particular group of oncogenes is known as ras, which have been identified in mammals, birds, insects, mollusks, plants, fungi and yeasts. The family of mammalian ras oncogenes consists of three major members (“isoforms”): H-ras, K-ras and N-ras oncogenes. These ras oncogenes code for highly related proteins generically known as p21ras. Once attached to plasma membranes, the mutant or oncogenic forms of p21ras will provide a signal for the transformation and uncontrolled growth of malignant tumor cells. To acquire this transforming potential, the precursor of the p21ras oncoprotein must undergo an enzymatically catalyzed farnesylation of the cysteine residue located in a carboxyl-terminal tetrapeptide. Therefore, inhibitors of the enzymes that catalyze this modification, i.e. farnesyl transferase, will prevent the membrane attachment of p21ras and block the aberrant growth of ras-transformed tumors. Hence, it is generally accepted in the art that farnesyl transferase inhibitors can be very useful as anticancer agents for tumors in which ras contributes to transformation.
Since mutated oncogenic forms of ras are frequently found in many human cancers, most notably in more than 50% of colon and pancreatic carcinomas (Kohl et al., Science, vol 260, 1834-1837, 1993), it has been suggested that farnesyl tranferase inhibitors can be very useful against these types of cancer.